1. Field of the Invention
The present invention relates to a method for manufacturing a piezoelectric resonant component, more particularly, to a method for manufacturing a piezoelectric resonant component having a cavity formed around a vibrating electrode of a piezoelectric resonant element.
2. Description of the Prior Art
FIG. 2 is a plan view showing an example of a conventional piezoelectric resonant element which is a background of the present invention and to which the present invention is applied. The piezoelectric resonant element 1 includes, for example, a rectangular piezoelectric substrate 2 made of ceramic or the like. At the center of one main surface of the piezoelectric substrate 2 and at the center of the other main surface thereof, for example, circular vibrating electrodes 3a and 3b are respectively formed in such a manner that the vibrating electrodes 3a and 3b are opposed to each other and the piezoelectric substrate 2 is sandwiched therebetween. A drawing electrode 4a is formed so as to extend from one end of the main surface of the piezoelectric substrate 2 to the vibrating electrode 3a, while a drawing electrode 4b is formed so as to extend from the other end of the other main surface thereof to the vibrating electrode 3b. To each of the drawing electrodes 4a and 4b, for example, one end of each of long lead terminals 5a and 5b is soldered.
FIGS. 3(A)-3(C) are sectional illustrative views showing an example of a conventional method for manufacturing a piezoelectric resonant component using the piezoelectric resonant element shown in FIG. 2. In the conventional method, first, as shown in FIG. 3(A), wax 6 such as paraffin wax, micro-crystalline wax or the like is dripped around the vibrating electrodes 3a and 3b of the piezoelectric resonant element 1.
Then, as shown in FIG. 3(B), an outer coating resin 7 is applied around the piezoelectric resonant element 1 and the wax 6. The outer coating resin 7 is made of a thermosetting resin, a solvent having a low boiling point, and a filler mixed with each other.
Then, the wax 6 positioned around the vibrating electrodes 3a and 3b is dispersed to the outside, and the outer coating resin 7 is cured. As a result, as shown in FIG. 3(C), a cavity 8 is formed around the vibrating electrodes 3a and 3b, and an outer coating material 9 is formed around the piezoelectric resonant element 1 and the cavity 8. In this case, first, the outer coating resin 7 is dried at a low temperature, thereby the solvent contained in the outer coating resin 7 is dispered to the outside. As a result, pores are formed on paths of the outer coating resin 7 through which the solvent is dispersed. Then, the whole is heated to cure the outer coating resin 7. When heating, the wax 6 is absorbed into the pores of the outer coating resin 7 and dispersed to the outside, thereby the cavity 8 is formed around the vibrating electrodes 3a and 3b. As a result of the heating of the whole, the outer coating resin 7 is cured, the outer coating material 9 is formed around the piezoelectric resonant element 1 and the cavity 8, and the wax 6 absorbed into the outer coating resin 7 is dispersed to the outside. Thus, in the conventional method shown in FIGS. 3(A)-3(C), the piezoelectric resonant component having the cavity 8 formed in the outer coating material 9 around the vibrating electrodes 3a and 3b of the piezoelectric resonant element 1 is manufactured.
However, in the conventional method shown in FIGS. 3(A)-3(C), since the pores are formed in the outer coating resin 7 by dispersing the solvent contained in the outer coating resin 7 to the outside, it is necessary to dry the outer coating resin 7 sufficiently. Thus, the conventional method is low in productivity.
Also, in the conventional method shown in FIGS. 3(A)-3(C), when the outer coating resin 7 is dried, since much flammable solvent is dispersed to the outside, there is a danger from fire.
Furthermore, in the conventional method shown in FIGS. 3(A)-3(C), there is a possibility that the pores are not formed sufficiently in the outer coating resin 7. In this case, the wax 6 remains around the vibrating electrodes 3a and 3b. Even though the pores are formed sufficiently in the outer coating resin 7, there is a possibility that the wax 6 is not absorbed into the pores and remains around the vibrating electrodes 3a and 3b. When the wax 6 has remained around the vibrating electrodes 3a and 3b, the characteristic of the piezoelectric resonant component is deteriorated.
Moreover, in the piezoelectric resonant component manufactured by the conventional method shown in FIGS. 3(A)-3(C), when the piezoelectric resonant component is washed with water, since the outer coating material 9 is porous, there is a possibility that water penetrates into the cavity 8 through the outer coating material 9. Since the diameters of pores of the outer coating material 9 communicating with the cavity 8 are small, it is difficult for the water which has penetrated into the cavity 8 to leave the cavity 8. Thus, the piezoelectric resonant component has a low water-resistant performance.